Thanks for the answer, Neil
The content of pResult was null while debugging, and the catch clause was not being called. I did not tried to use the tool window in ArcMap, and when I did it I realize the real issue: The type of the .lyr files. They were not features classes, nor feature layers, nor shapefiles, the only types accepted by ExportCad(). Whitout your question, I would not realize that.
So, now my work is to figure out why the .lyr files are not saved as feature classes, in order to be able to export them. I still can't export neither using the tool nor the code, except for the small files I mentioned, but these ones are defined as feature classes, unlike that ones.
Thanks so much.
Rodrigo Salvador
COPEL
Geoprocessing Developer
Curitiba, PR, Brazil
+55 (41) 84038660